1. Field of the Invention
The present invention relates to a photoconductive encoder structure, and especially to a photoconductive encoder with more cogs surrounded a grating cogwheel and a better focusing effect of a light source. Furthermore, the production process of the grating cogwheel is more convenient.
2. Description of Related Art
A prior art mouse comprises an X-axis encoder and a Y-axis encoder with output logic sequence signals such as, for example, 11, 10, 00, 01. The mouse is placed on a top or other surface of a desk and is moved in designated directions to move a cursor on a monitor to corresponding positions. The movement of the cursor on the monitor made by the mouse adopts a principle that the X-axis and the Y-axis encoders together produce control signals to move the cursor.
Reference is made to FIG. 1; an encoder mainly comprises a light source 60, an encoder wheel 65, and a sensor (using two juxtaposed sensing chips S1 and S2 to produce phase signals) 70. When the encoder is in operation, light emitted by the luminescence element 60 and received by the sensor 70 is sheltered or not sheltered by the encoder wheel 65. The sensor 70 generates sequence signals including OFF (0) and ON (1). For example, when the grating cogwheel 65 rotates clockwise, the sensor 70 generates repeated and continuous sequence signals 111000011 . . . ; and when the grating cogwheel 65 rotates counterclockwise, the sensor 70 generates repeated and continuous sequence signals 01001011010001 . . . for circuit encoding.
Reference is made to FIG. 2A and FIG. 2B, in which the grating cogwheel 65 comprises a housing 67 having square cogs 66. A cylinder 68 with a cylindrical space defined therein protrudes from the center of the housing 67. A plurality of bumps 69 are set on the corresponding square teeth 66 along the circumference of an incident surface on the housing 67. Therefore, the light emitted by the luminescence element 60 is projected on the incident surface of the grating cogwheel 65 and then focused. The focused light is refracted by a triangle-shaped section 671 to the top of the square cogs 66 and then projected to the sensor 70. Because of the rotation of the grating cogwheel 65, the sensitization chips S1 and S2 produce OFF (0) and ON (1) sequence signals for circuit encoding.
The depth and the width of the two adjacent square cogs 66, and the numbers of the granules 69 in the structure of the grating cogwheel 65, are also important factors in the production process. Therefore, the numbers of the square cogs 66 and the granules 69 on the grating cogwheel 65 are limited to a fixed value.